George Bush and Tony Blair speak to reporters after a White House meeting about Iraq in December 2006. Photograph: Kevin Lamarque/REUTERS

Following 9/11, Tony Blair had regular fortnightly video conferences with President George Bush. On one occasion, after a series of leaks of letters from the British side recording previous sensitive discussions, Bush stopped in mid-sentence, looked down the camera at the young official taking notes at the No 10 end and said: "Write that down carefully. I want to read it right when it is leaked."

It is very difficult to conduct diplomacy effectively when your confidential deliberations are made public in this way. Mutual trust is the basis of such relations and once that trust is breached, candid conversations are less likely. It is like having a conversation in the pub with your best mate about problems with your girlfriend and then finding the content, possibly with a bit of spin added, posted on the internet. You won't be having that conversation again any time soon. And yet, unlike the conversation in the pub, governments do have to talk to each other, and being able to talk to each other frankly in private is essential to preserving their country's security and promoting its prosperity.

The leak of a quarter of a million state department cables will undoubtedly make life difficult for US diplomats for some time to come. A British official having lunch with an American diplomat in a West End restaurant today will think twice before telling him or her something really interesting for fear of seeing it in print. More significantly, there will be a huge amount of damage limitation to undertake in Afghanistan and the Arab world in particular.

On the whole it is surprising how few real surprises seem to be contained in quite such a huge amount of material. To that extent we can feel reassured that the US is not in fact conducting a secret policy around the world that we knew nothing about before.

Even the revelations made so far are not that shocking. It comes as no great surprise that Arab states fear Iran, and want the US to do something about it. The reports will embarrass governments by showing they say one thing in public and another in private, but they are not alone in that. The US embassy assessments of individuals and governments elsewhere will be cringe-making for subjects and authors – but not totally unexpected. I know how they feel, having had my embarrassing emails published repeatedly during the inquiries in Blair's time as PM. Clever comments don't look quite so good when they are published in the cold light of day.

That embarrassment will pass, however. As a young diplomat in post-revolution Lisbon I used to send telegrams back after lunches with communist deputies, and I am impressed with the coherence of the state department reporting by comparison. On the whole these cables are well-judged and well-written and show good political insights – particularly those from William Burns in Moscow. Thinking back, the thing that was notable about the leaks of the secret letters recording Blair's conversations with the American president was that although they caused Bush temporary embarrassment at home, they did not prevent him carrying on being frank, often alarmingly so, in subsequent video conferences. In this case, too, normal relations will be rapidly resumed.

This is not a comprehensive set of cables from US posts. Those being published by WikiLeaks seem mostly to have been chosen rather randomly. They are mostly run-of-the-mill reports of meetings with officials, visits by congressional delegations, assessments of the political situation in the country concerned or meetings with foreign ministries on policy issues. Many of the cables you would have expected to see, for instance analyses of British politics leading up to the general election, are missing. (Although there is one of the outcome of the Welsh elections and its implications for the Labour party and Plaid Cymru: hard to believe there were many readers for that in Washington.) The most sensitive reports, such as those of Hillary Clinton, or of President Obama's conversations with world leaders, or descriptions of the most sensitive Middle East negotiations, are not included.

But in case we revel in someone else's embarrassment too freely, we should bear in mind that the real danger in these leaks lies not in western democracies, where bruised feelings about waspish comments on David Cameron or Nicolas Sarkozy will be rapidly salved, but in non-democracies and in unstable regions of the world. If I were the source quoted in some of the reporting cables from Moscow or from Arab capitals I would live in real fear that my name would come out if WikiLeaks decided to publish unredacted versions. In the case of these cables the old cliche is true: the devil is in the detail. Out of context they may not make great headlines in the west, but hidden away in them are subjects that are really important to individual countries or governments.

And while bruised feelings may be rapidly healed in the west, they will not be resolved so quickly in other countries not used to the leak as a fact of political life. Afghanistan's President Karzai or King Abdullah of Saudi Arabia may take the issue much more seriously than Angela Merkel or Silvio Berlusconi.

While I accept there are good public interest reasons for individual leaks – even though I used to hate them when they made my life more difficult in government – I find it hard to see what public interest there is in a leak on this industrial scale. Even if individual cables reveal individual duplicity, the great mass do not. Their release simply makes the job of government harder and potentially puts the lives and careers of innocent individuals in countries other than the US at risk for no very good reason other than political voyeurism.

The leaks will clearly make the Americans look again at the security of their cable traffic, and I assume the site carrying the cables has been taken down. It is understandable that the US wanted to encourage information-sharing after 9/11 to try to reduce the chance of threats passing undetected, but having a huge database like this accessible to a 22-year-old private in Iraq to come in and download while pretending to listen to Lady Gaga on his CD player was crazy.

While this leak may change security rules, I confidently predict it will not change diplomacy, which has been based on the secret exchange of confidences between individuals and governments for many centuries. We have not yet found a better way of arranging human affairs, and I doubt we ever will.